1. Field of the Invention
The present invention relates to a structure of a bearing housing of a cylinder block of an internal combustion engine and more particularly to a bearing housing formed by material having a thermal expansion coefficient different from that of a crankshaft.
2. Description of Background Arts
There is an engine whose cylinder block is cast in aluminum alloy to reduce the weight of the engine. A plurality of bearing housings provided in the cylinder block and an iron-made crankshaft is supported at crank journals thereof by the bearing housings through metal bearings. When the engine is operative, heat produced by combustion of mixture gas is transmitted to the bearing beds of the cylinder block. As a result, the temperature of the bearing housings increases to expand clearances between the aluminum alloy made bearing housings and the crank journals, this causing noises and vibrations from the engine.
Japanese Patent Application Laid-open No. TokuKai-Hei 10-159648 discloses a technique in which light weight aluminum alloy made bearing caps having a low thermal expansion coefficient and high rigidity are joined by supersonic soldering to the bearing housings. Also, the patent application discloses an embodiment of a bearing cap made of fiber reinforced aluminum alloy. The bearing cap has the same width as that of the bearing housings and a bearing cap is jointed to the respective bearing housings.
According to the prior art, since the bearing cap is made of aluminum alloy having a low coefficient of thermal expansion, the difference between a coefficient of thermal expansion of the bearing housings and that of the crank journals can be reduced. Therefore, since the clearance between the crankshaft and the bearing surface is kept in an appropriate level irrespective of temperature changes, the problem of vibrations and noises can be solved.
Further, Japanese Patent Application Laid-open No. Toku-Kai 2000-205037 discloses a technique wherein a bulkhead for connecting left and right walls of a cylinder block and for supporting a bearing housing has a fiber reinforced preform integrally cast almost over the full length in a transverse direction between the left and right walls of the cylinder block and accordingly a fiber reinforced metal (FRM) area is formed around a part where the preform is integrally cast. As a result, the bulkhead having high rigidity damps vibrations of the left and right walls and at the same time prevents thermal expansion of the bearing surfaces.
The bearing housing is required to have adequate strength and rigidity because impact loads caused by the combustion of air-fuel mixture is directly applied to the bearing housing. The method of integrally casting a piece of large preform laterally extending over the full length of the bulkhead between the left and right outer walls of the cylinder block as described in Toku-Kai 2000-205037 has a disadvantage that since the preform itself has a large volume and molten aluminum inadequately impregnates into the preform, sometimes cavities are produced in the preform. The bearing housings containing cavities therein have large dispersions in thermal expansion coefficients and provide inadequate strength and rigidity. On the other hand, in case where the volume of the preform is decreased in order to avoid such incovenience, it becomes difficult to attain an original object of properly controlling the clearance between the crank journals and bearing surfaces.
It is an object of the present invention to provide bearing housings having high strength and rigidity and capable of reducing the difference of thermal expansion coefficients between bearing housings (bearing surfaces) and crank journals.
To achieve the object, the structure of bearing housings comprises aluminum alloy for constituting a whole cylinder block and a plurality of fiber reinforced metal areas containing reinforced metal fibers integrally cast with aluminum alloy separately in an axial direction of a crankshaft.